1. Field of the Invention
The present invention relates to a failure determination device for a cell voltage monitor which detects voltages of a plurality of single cells connected in series.
2. Description of the Related Art
In recent years, a fuel cell including a polymer electrolyte fuel cell (PEFC) has been developed in earnest. The polymer electrolyte fuel cell is provided with an anode and a cathode. The anode is provided with hydrogen (fuel cell gas) and the cathode is supplied with oxygen (oxidant gas) to cause an electrochemical reaction to generate electricity. Because each fuel cell has a low output, and the fuel cell includes a plurality of single cells, a fuel cell stack to form the plurality of single cells connected in series and stacked has widely been used.
However, a generation of an electricity by the single cell cannot be measured from an output current or an output voltage of the fuel cell stack. Accordingly, a cell voltage monitor which detects a voltage of a single cell (cell voltage) is connected with each single cell, thereby the generation of an electricity by the single cell is measured (refer to JP-2004178899). When a cell voltage steps down and the generation of an electricity by the single cell is decreased, the generation of an electricity by each single cell is restored by airing in order to remove excessive water attached on the surface of a membrane electrode assembly (MEA).
The cell voltage monitor has a minimum value of a cell voltage (minimum value cell voltage) in a detectable range depending on a voltage detection circuit. A failure determination device for the cell voltage monitor determines that the cell voltage monitor has a failure when a detected cell voltage is equal to the minimum value cell voltage.
Therefore, the cell voltage monitor cannot determine whether or not the minimum value cell voltage is brought by a failure. A detected cell voltage is equal to or lower than the minimum value cell voltage when a part of the cell voltage monitor has a failure (for example, due to disconnection of a wiring harness). In addition, a cell voltage of a single cell (fuel cell stack) also becomes equal to or lower than the minimum value cell voltage when a demand for generating electricity is reduced. In the end, the failure determination device for the cell voltage monitor determines that the cell voltage monitor without a failure is damaged when the minimum value cell voltage is detected in the process of a normal voltage drop due to a low demand of generating electricity.